Conventionally, every time a stepper motor is stopped, power must be applied to maintain a stationary or holding position. Occasionally, this power may be applied for long periods of time. This power is typically called hold current.
Further, most stepper motor applications have a function that brings the motor to a known “home” position. Typically, after the motor is homed, a hold current is applied for long periods of time, such as several hours, to ensure that the motor does not lose position. After functional moves have been performed, the motor returns to this hold current. The energy to maintain this position is wasted as heat, although this measure is necessary to prevent inadvertent movement of the motor by vibration or other sources of movement.
Moreover, the stepper motor is generally homed when a positioning function starts, as the motor position may have changed while the motor was off. Consequently, every time the stepper motor loses power, it must be re-homed when it is started again. Depending on how far away the home position is, the stepper motor may take a long time, as much as several seconds, to reach that position and that operation may also be noisy.
It would be highly desirable to lock the stepper motor in place without a continuous power requirement for that functionality. This way, when the motor is started again, the stepper motor system would already be in the correct position and the need for a homing operation would be eliminated.